This invention relates to steam turbines. More particularly, it relates to low pressure steam turbines wherein steam generally flows axially through rows of radially extending stationary blades supported by outer blade rings and rotatable blades mounted on a rotor to an exhaust guideway directing the steam from the last row of blades toward an exhaust.
Generally speaking, the power output of a steam turbine is a function of several known variables importantly including the steam flow rate. Thus, it has been proposed to increase the steam flow rate and thereby enhance the power output of existing low pressure turbines by replacing the rotatable blades in the last row of the turbines with longer blades. A significant increase in steam flow rate would be realized by replacing the original rotatable blades with rotatable blades which radially extend beyond the stationary blade assembly. However, this would require that steam flow-guiding surfaces of the outerblade ring supporting the stationary blades be extensively machined to provide a more outwardly directed flow-guiding surface for guiding the steam to the tips of the replacement rotatable blades. Extensive machining of the outer blade ring of an existing turbine and a carrier ring which conventionally supports the outer blade ring will remove the juxtaposed downstream ends of the outer blade ring and the carrier ring which conventionally provides bearing support to secure the stationary blades and the outer blade ring against axially directed pressures on the blades. In addition, an exhaust flowguide conventionally bolted to the carrier ring of an existing turbine cannot be realigned with the carrier ring if the replacement rotatable blades radially extend beyond the outer blade ring supporting the stationary blades.
It is an object of the invention to provide a steam turbine with flow-guiding surfaces guiding steam to and from a row of rotatable blades which extend radially beyond outer blade ring supporting the axially adjacent upstream row of stationary blades.
It is a further object of the invention to provide support for the gas flow-guiding surfaces in flow communication with relatively long rotatable blades.